diff --git a/internal/2017/DayOne/code_test.go b/internal/2017/DayOne/code_test.go
new file mode 100644
index 0000000..1140d4d
--- /dev/null
+++ b/internal/2017/DayOne/code_test.go
@@ -0,0 +1,41 @@
+package dayone
+
+import "testing"
+
+func TestPartOne(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    []int
+		expected int
+	}{
+		{
+			name:     "1122 produces 3",
+			input:    []int{1, 1, 2, 2},
+			expected: 3,
+		},
+		{
+			name:     "1111 produces 4",
+			input:    []int{1, 1, 1, 1},
+			expected: 4,
+		},
+		{
+			name:     "1234 produces 0",
+			input:    []int{1, 2, 3, 4},
+			expected: 0,
+		},
+		{
+			name:     "91212129 produces 9",
+			input:    []int{9, 1, 2, 1, 2, 1, 2, 9},
+			expected: 9,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := PartOne(tt.input)
+			if got != tt.expected {
+				t.Errorf("PartOne() = %d, want %d", got, tt.expected)
+			}
+		})
+	}
+}